This invention relates to fuel-measurement devices, and particularly to a device for determining the quantity of fuel in a fuel tank. More particularly, this invention relates to a non-linear fuel-level indicator that is movable within the fuel tank and has a continuity circuit that includes a coded resistance pattern representative of internal fuel tank dimensions and a buoyant continuity bridge for short-circuiting the coded resistance pattern to provide a value of resistance indicative of the fuel level and the corresponding instantaneous fuel volume in the fuel tank.
Known fuel gauges having a continuity circuit and a floating fuel depth sensor generally provide only a linear model of the "volume profile" (i.e. internal dimensions) of the fuel tank. Although such a system is able to indicate generally the presence of fuel in the fuel tank, the indication does not provide extremely accurate information regarding the exact quantity of fuel remaining in the fuel tank, especially at very low fuel levels and in a fuel tank having a non-linear volume profile. Vehicle operators will appreciate the fuel-management problems associated with these known linear fuel gauges.
One object of the present invention is to provide a fuel gauge that is able to measure accurately the quantity of fuel in a fuel tank in which the quantity of fuel therein varies in non-linear relation to the depth of fuel within the fuel tank due to a non-linear volume profile of the fuel tank.
Another object of the present invention is to provide a fuel gauge that is able to measure most accurately the remaining quantity of fuel in the fuel tank at very low fuel levels. At that stage, information regarding available fuel supplies is of critical importance to a fuel consumer and must be monitored and determined with substantial accuracy to guard against unexpected fuel shortages.
In accordance with the present invention, an apparatus is provided for determining the quantity of fuel in a fuel tank having a contoured interior wall. The quantity of fuel in the fuel tank is defined by the contour of the interior wall below the top surface of the fuel in the fuel tank. The apparatus includes means for measuring the depth of fuel at a measurement location within the fuel tank and providing a value of resistance indicative of the measured depth, and indicator means for interpreting the resistance provided by the measuring means to determine the instantaneous quantity of fuel in the fuel tank.
The measuring means includes a buoyant member for floating on the top surface of fuel in the fuel tank, a conductor supported on the buoyant member to float therewith, and a pattern of resistance in electrical contact with the floating conductor. The pattern of resistance is selected to correspond to the contour of the interior wall. Thus, the resistance pattern is coded to represent the volume profile of the fuel tank. The coded resistance pattern is selected to represent the variation in the volume of the fuel tank due to the shape of the interior wall of the fuel tank as a function of fuel depth at a selected measurement location within the fuel tank.
The measuring means further includes means for applying a voltage across the conductor and the pattern of resistance. The floating conductor and the pattern of resistance cooperate to provide a value of resistance corresponding to the depth of fuel in the fuel tank at the measurement location. The indicator means interprets that value of resistance to determine the instantaneous quantity of fuel in the fuel tank.
In preferred embodiments of the present invention, the pattern of resistance includes an electrically conductive path and a plurality of spaced-apart resistors electrically coupled in series along the path. The value of each resistor and the spacing between each pair of adjacent resistors along the path cooperate to define an electrical circuit model of the contour of the interior fuel tank wall. Calculated selection of the resistance values and resistance spacing encodes the pattern of resistance so that it represents either a linear or non-linear function matching the exact contour of the interior fuel tank wall.
The apparatus further includes means for moving the coded pattern of resistance within the fuel tank to position the resistance pattern in about a predetermined aligned relation to the contour of the interior fuel tank wall. In this way, the pattern of resistance is automatically positioned relative to a reference datum in close proximity to the bottommost wall of the fuel tank. Such an alignment operates to calibrate the apparatus in that the electrical model defined by the pattern of resistance is positioned to match the contour of the fuel tank, thereby permitting the floating conductor to rise and fall with the fuel level in the fuel tank while maintaining electrical contact with the coded pattern of resistance. The floating conductor provides an accurate indication of the depth of fuel in the fuel tank at the measurement location. In one preferred embodiment, the moving means comprises a fuel-sending unit submerged within fuel in the fuel tank and movable using fuel pressure generated by a fuel pump toward lowermost regions of the fuel tank.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.